T-lymphocyte activation antigen CD86 (CD86; B7-2; B70) is type 1 transmembrane protein with an extracellular domain containing two Ig-like domains and shares ~25% sequence identity with CD80 (B7-1). (1) CD86, together with CD80 and B7-H2, serves as a ligand for CD28 and CTLA-4. (2) (3) Although CTLA-4 binding to ligands is stronger than CD28 binding, when in competition, CD86 has a relative preference for CD28 compared to CD80, which binds very strongly to CTLA-4. (4) Binding of CD86, CD80 or B7-H2 to CD28 delivers a positive signal to T cells, promotes proliferation and cytokine secretion and also results in up-regulation of IL-6 production by dendritic cells, causing immunostimulatory activity. (5) In contrast, the interaction of CTLA-4 with B7 ligands attenuates T cell activation and induces T cell anergy and additionally up-regulates IFN-γ resulting in tryptophan catabolism and suppression of T cell proliferation. (5) CD86 is constitutively expressed on the cell surface of the antigen-presenting cell (APC) and is rapidly up-regulated upon interaction with CD28 as opposite to the CD80 which is expressed inducibly. (5)

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